Grinding machine having an adaptive control system

ABSTRACT

A grinding machine is provided which is capable of decreasing the grinding resistance exerted on the grinding wheel thereof towards an objective grinding resistance as a number of grinding operations proceed. A current optimum grinding resistance is calculated on the basis of the objective grinding resistance and the number of grinding operations. The feeding speed of the grinding wheel is controlled such that the grinding resistance exerted on the grinding wheel may be maintained equal to the current optimum grinding resistance.

ilnited States Patent Wada et a1.

Apr. 24, 1973 GRINDING MACHINE HAVING AN ADAPTIVE CONTROL SYSTEM Inventors: Ryuji Wada; Hideo Nishimura, both of Kariya; Hayashi Kodama, Takahama; Taisuke Kawamata, Kariya, all of Japan Toyoda Koki Kabushiki Kariya-shi, Aichi-ken, Japan Filed: Dec. 6, 1971 App]. No.: 205,150

Assignee: Kaisha,

Foreign Application Priority Data Dec. 19, 1970 Japan ..45/l 14509 U.S. Cl ..5l/165.77, 5 l/l65.88 Int. Cl. ..B24b 49/16 Field of Search ..5l/l39, 165 R, 165.77,

[56] References Cited UNITED STATES PATENTS 3,524,285 8/1970 Rutt ..5l/l 39 X 2,946,162 7/1960 Mader ..5l/l65.88

Primary ExaminerHarold D. Whitehead Atl0rneyNorman F. Oblon et al.

A grinding machine is provided which is capable of decreasing the grinding resistance exerted on the grinding wheel thereof towards an objective grinding resistance as a number of grinding operations proceed. A current optimum grinding resistance is calculated on the basis of the objective grinding resistance and the number of grinding operations. The feeding speed of the grinding wheel is controlled such that the grinding resistance exerted on the grinding wheel may be maintained equal to the current optimum grinding resistance.

ABSTRACT 5 Claims, 6 Drawing Figures Patented April 24, 1973 3,728,826

4 Sheets-Sheet. 1

'IVNHLVN GHAONBZI JO HHITTOA Patented 'April 24, 1973 4 Sheets-Sheet 2 4 Sheets-Sheet l GRINDING MACHINE HAVING AN ADAPTIVE CONTROL SYSTEM BACKGROUND OF THE INVENTION 1. Field Of The Invention:

The present invention relates to a grinding machine having an adaptive control system, wherein the feeding speed of a grinding wheel thereof is controlled such that the grinding resistance exerted on the grinding wheel is suitably maintained for continuously changing grinding conditions.

2. Description Of The Prior Art:

In the prior art grinding machines having an adaptive control system, the feeding speed of the grinding wheel thereof was controlled such that the grinding resistance was maintained at a required optimum value. While such prior art grinding machines have proven to be somewhat effective in improving grinding efficiency, they still are incapable of producing finished products of excessive high quality.

A need existed, therefor, for the development of an improved adaptive control system which would increase the grinding efficiency and effectively enable consistent high quality products to be produced.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a grinding machine having a new and improved unique adaptive control system.

Another object of the present invention is the provision of a new and improved unique adaptive control system which is effective to consistently produce high quality products with a high grinding efficiency.

A further object of the present invention is the provision of a new and improved unique adaptive control system for a grinding machine wherein the grinding resistance exerted on the grinding wheel thereof is decreased towards an objective value as the grinding operations proceed.

Yet one other object of the present invention is the provision of a new and improved unique adaptive control system for a grinding machine which causes a dressing device to dress the grinding wheel when the volume of material removed from a workpiece by grinding operations becomes equal to a predetermined amount.

Briefly, in accordance with the present invention, the foregoing and other objects are in one aspect attained by the provision of a grinding machine wherein an adaptive control system is provided for decreasing the grinding resistance exerted on the grinding wheel thereof towards an objective grinding resistance provided by a control circuit as the grinding operations proceed. A current optimum grinding resistance is calculated on the basis of the objective grinding resistance and the number of grinding operations and the feeding speed of the grinding wheel is controlled such that the grinding resistance exerted on the grinding wheel is maintained equal to the current optimum grinding resistance. Moreover, means are provided such that when the amount of material removed from a workpiece being ground reaches a predetermined detected volume, a dressing device will dress the grinding wheel of the grinding machine.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects of the present invention will become more fully apparent from the following detailed description of a preferred embodiment of the present invention with reference to the accompanying drawings, in which:

FIG. I is a graph showing the relationship between the volume of removed material from a workpiece and the unit resistance;

FIG. 2 is a block diagram showing a control system applied to a grinding machine according to the present invention;

FIG. 3 is a block diagram showing an adaptive control system of the present invention;

FIG. 4 is a diagram showing how to measure the amount of grinding wheel wear;

FIG. 5 is a block diagram showing an operation circuit for calculating a current optimum unit resistance; and,

FIG. 6 is a sectional view of a sizing device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Before describing a preferred embodiment of the present invention, reference will be made to FIG. 1 wherein the relationship between the volume of material removed from a workpiece and the grinding resistance exerted on a grinding wheel per unit of width, hereinafter referred to as unit resistance is shown. The line ZL shows that the marginal total volume of material, which can be removed in accordance with grinding operations which take place from just after a dressing of the grinding wheel until the appearance of a grinding burn or chatter marks on the ground surface, varies in accordance with the variation of the unit resistance. The line ZI-Is shows the relationship between the unit resistance and the total volume of material, which can be removed in accordance with grinding operations which begin after a dressing of the grinding wheel under conditions wherein the roughness of the ground surfaces are kept within a desired grade l-Is. The lines ZI-Ir and 2H! respectively show relationships similar to that of the line ZI-Is, but under different respective grades I-Ir and H! of surface roughness. In order to grind workpieces with high efficiency and low cost, it is necessary to increase the unit resistance and the total volume of the removed material. However,as shown in FIG. I, if the unit resistance is increased, then the total volume of the removed material will decrease.

In consideration of the above, the feeding speed of the grinding wheel has been controlled so that the unit resistance is maintained at an objective unit resistance fs which is shown as corresponding to the intersecting point P between the lines ZL and ZI-Is. While somewhat satisfactory, one problem with maintaining the unit resistance constant is that a product of excessively high quality will be produced such that the roughness of the ground surfaces thereof are held until the volume of the removed material reaches the value 21 within the grade I-Ir instead of the desired grade Hs. Such early efficient grinding operations tend to waste labor and are therefore disadvantageous to the overall grinding efficiency.

In the grinding machine according to the present invention, the unit resistance is established during a first grinding operation which takes place just after a dressing of the grinding wheel at an initial unit resistance fo which is larger than the objective unit resistance fs, whereby the roughness of the ground surface is held within the desired grade H5. The unit resistance is thereafter accordingly decreased towards the objective unit resistance fs as the grinding operations proceed.

Referring now to the other Drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, and more particularly to FIG. 2 thereof, wherein is shown a bed 40 on which a table 5 is slidably mounted. A pulse motor 5b is secured on the bed 40 and rotates a feed screw which is threadedly engaged with the table 5 so that the table 5 may be moved on the bed 40. The table 5 carries a spindle head 7 and a tail stock thereon. A work spindle, not shown, is rotatably carried on the spindle head 7 and is driven by a hydraulic motor 7b. A workpiece W is supported between the centers of the spindle head 7 and the tail stock, and rotation of the work spindle is transmitted thereto by a driving dog. The rotational frequency of the hydraulic motor 7b is controlled by a conventional electro-hydraulic servovalve 7a. A sizing device 9, which measures the diameter of the workpiece W,is slidably mounted on the table 5 and can be moved toward and away from the workpiece W by a hydraulic cylinder, not shown. The sizing device 9 includes a pair of feelers 41a and 41b and an electric measuring device for measuring the distance between the feelers. A counter 46 is connected to the sizing device 9 and serves to indicate the workpiece diameter in digital numbers. This is accomplished by the sizing device 9 which internally changes the analog value measured to a digital value and supplies the same to the counter 46. The details of the sizing device will be later described with reference to FIG. 6.

A grinding wheel 42 is mounted on a spindle which is rotatably supported by a wheel head 6 through a hydraulic bearing which is fixedly mounted thereon. The grinding wheel 42 is connected to a motor, not shown, which is mounted on the wheel head 6 and rotates the grinding wheel 42. A slide base 43 is mounted on the head 40 and is slidable in a direction perpendicular to the table 5. The wheel head 6 is, in turn, slidably mounted on the slide base 43 in a parallel relationship therewith. A pulse motor 6b is secured on the slide base 43 and rotates a feed screw 44 which is threadedly engaged with the wheel head 6 so that the wheel head 6 may be moved toward and away from the workpiece W. A conventional dressing device 8 for dressing the grinding wheel 42 is mounted on the wheel head 6. A conventional grinding wheel compensating apparatus 12 is secured on the bed 40 and rotates a compensating screw 45 which is engaged with the slide base 43 so that the slide base 43 may be moved toward the workpiece W. The operation of the grinding wheel compensating apparatus 12 will not be explained in detail, since such apparatus is well known to those skilled in the art and for an understanding of the present invention it is sufficient to appreciate that the grinding wheel compensating apparatus 12 serves to move the slide base 43 toward the workpiece W by an amount equal to that of the dressing of the grinding wheel 42.

It should be understood that the pulse motors 5b and 6b are respectively connected to pulse motor drive circuits 5a and 6a which are, in turn, responsive to a conventional numerical control device 2. lnforrnation for properly controlling the operation of the pulse motors 56 and 66 and an adaptive control system 3, explained hereinafter, are stored on a tape, not shown, and read by a tape reader 1 which serves to transmit the information read from the tape to the numerical control device 2. The details of the tape reader 1 and the numerical control device 2 will not be given,since the same are conventional and may be, for example, the numerical control system manufactured by Fujitsu, Ltd., Kawasaki, Japan, and sold as FANUC MODEL 260.

A pressure differentiator 10 is provided and is responsive to the pressure differential which is produced by the grinding resistance F exerted on the grinding wheel 42 between the front and rear pressure pockets of the hydraulic bearing. It should be appreciated that the pressure differentiator 10 is conventional and may be of the type which changes pressure differential into an electric signal. The output of the pressure differentiator 10 is applied to the adaptive control system.

A preset device 47 is provided and numerically contains digital information corresponding to the distance between the axis of the workpiece W and the front surface of the grinding wheel 42 at its retracted position. A conventional contactless microswitch 77 is mounted on the slide base 43 and generates an electric signal to open a gate circuit 48 when the wheel head 6 moves to the retracted position. In accordance with the electric signal generated,the value or number preset in the present device 47 is transmitted and registered in a counter 49. The counter 49,which is connected to the numerical control system 2 and to the adaptive control system 3, subtracts the number of electric pulses supplied to the pulse motor 6b from the value or number registered therein, and thus indicates the current distance L between the grinding surface of the grinding wheel 42 and the axis of the workpiece W.

Referring now to FlG.3,an adaptive control system 3 is shown as including a revolution control device 20 which is connected to the numerical control system 2 and to the counter 46 which is connected to the sizing device 9. The revolution control device 20 calculates the rotational frequency 11 of the work spindle according to the following equation:

where Vs the desired peripheral speed of the workpiece W given by the numerical control system 2 and d0= the workpiece diameter measured by the sizing device 9. The digitally calculated rotational frequency n is applied to a digital-to-analog converter 21 for conversion into a corresponding voltage. The output voltage of the digital-to-analog converter 21 is'amplified by a conventional amplifier 22. The electro-hydraulic servovalve 70 controls the flow rate of the pressurized fluid supplied to the hydraulic motor 7b in accordance with the output voltage of the amplifier 22 so as to regulate the rotational frequency n of the hydraulic motor 7b.

A divider 19 is connected to the counter 46 for calculating oneihalf (do/2) of the workpiece diameter. A comparator 23 is connected to the divider 19 and to the counter 49 and serves to compare the one-half diameter (do/2) with the current distance L between the grinding surface of the grinding wheel 42 and the axis of the workpiece W, and will generate an output signal when the current distance L becomes equal to or smaller than the one-half diameter (do/2). A comparator 24 is connected to the counter 46 and to the numerical control system 2 for comparing the workpiece diameter (do) with the desired diameter (dj) of the finished workpiece as indicated by the numerical control system 2, and will generate an output signal when both diameters become equal to each other. A NOT circuit 25 is connected to the output terminal of the comparator 24 for inverting the output of the comparator 24. An AND circuit 26 is connected to the output terminals of the divider l9,the comparator 23 and the NOT circuit 25 and will allow the output of the divider 19 which represents the one-half diameter (do/2) to be transmitted to a subtracting circuit 28 when both the comparator 23 and the NOT circuit 25 generate output signals therefrom. An AND circuit 27 is connected to the output terminals of the counter 49,the comparator 23 and the NOT circuit 25 and will allow the output of the counter 49 which represents the current distance L to be transmitted to the subtracting circuit 28. The subtracting circuit 28 subtracts the current distance L from the one-half diameter (do/2).

It should be understood that the one-half diameter (do/2) and the current distance L will be equal when the grinding wheel 42 comes in contact with the workpiece W just after the dressing operation. However,as shown in FlG.4,if the grinding wheel 42 is worn away, the one-half diameter (do/2) will become larger than the current distance L when the grinding wheel 42 comes in contact with the workpiece W. It will be apparent that the difference between the one-half diameter (do/2) and the current distance L coincides with the amount 5 of wear of the grinding wheel 42. Since it is experimentally known that the amount of wear of the grinding wheel increases nearly proportional to the volume of the removed material,then the unit resistance will decrease as the grinding wheel wear increases in the embodiment of the present invention.

A counter 29 is connected to the subtracting circuit 28 and records the amount 5 of the grinding wheel wear. The counter 29 will be reset by the output signal of the comparator 24 every time a grinding operation is completed. An operation circuit 30 is provided for calculating a current optimum unit resistance (fv according to the following equation;

where fs the objective unit resistance, 6=the amount of the grinding wheel wear, 5l=the maximum amount of the grinding wheel wear and k a proper positive constant. As shown in FIG. 5,the operation circuit 30 includes a subtracting circuit 5l,a multiplier 52,an adding circuit 53 and a'driver 54. The subtracting circuit 51 is connected to the counter 29 and to a present circuit 50 wherein the maximum amount 81 of the grinding wheel wear and the proper positive constant k are numerically preset in digital form. The subtracting circuit 51 subtracts the maximum amount 81 of the grinding wheel wear from the amount 8 of the grinding wheel wear. The multiplier 52 is connected to the subtracting circuit 51 and to the preset circuit 50 and multiplies the difference 8 8 l by the constant k. The adding circuit 53 adds 1 to the output k (8 8 l) of the multiplier 52. The divider 54 divides the objective unit resistance fs, given by the numerical control system 2, by the output 1 k (8 8 l) of the adding circuit 53. Since the current optimum unit resistance fv is determined as described above,it should be understood that the same is changed from the initial unit resistance to (=fs/( l-k 81) to the objectiveunit resistance fs ,in accordance with any increase in the amount 8 of the grinding wheel wear. It should further be understood that the objective unit resistance fs will be changed in accordance with any alteration in the quality of the workpiece material.

The output fv of the operation circuit 30 is applied to a digital-to-analog converter 31 for conversion into a corresponding voltage which is applied to one terminal of a differential-input amplifier 32. A digital-to-analog converter 34 is supplied by the numerical control system 2 with the width b of the part to be ground and converts the digital information representative thereof into a corresponding electric voltage. A divider 33 is provided and divides the output of the pressure differentiator l0,which represents the grinding resistance F,by the output of the digital-to-analog converter 34,which represents the width b,so as to calculate a real unit resistance F/b. The real unit resistance F/b is applied to the other terminal of the differential-input amplifier 32 and is compared therein with the current optimum unit resistance fv. The differential-input amplifier 32 generates an output voltage corresponding to fv+ (fFF b). The bur ufialtage a ming plied to a pulse generator 35 which generates pulses having a frequency which is proportional thereto. The pulses at the output of the pulse generator 35 are applied to the pulse motor 6b by way of the pulse motor drive circuit 6a. The wheel head 6 is moved in accordance therewith toward the workpiece W,whereby the feeding speed of the grinding wheel 42 is controlled so. that the real unit resistance F/b may be maintained equal to the current optimum unit resistance fv.

An operation circuit 36 is provided for calculating the volume of the removed material 2 according to the following equation:

where b the width of the part to be ground, D0 the workpiece diameter before the grinding operation and df= the diameter of the finished workpiece provided by the numerical control system 2. The calculation of the volume of the removed material Z is performed when a signal which represents engagement of the pair of feelers 41a and 41b of the sizing device 9 with the periphery of the workpiece W, is applied to the operation circuit 36. Since the total volume of the removed materiaLwhich corresponds to the intersecting point P,shown in FIG. l,will vary when the quality of the workpiece material is changed,the calculated volume 2 of the removed material must be converted into the volume of a standard material. A multiplier 55 is provided for enabling the above conversion by multiplying the calculated volume Z of the removed material by a coefficient Kw provided by the numerical control system 2 and corresponding to the quality of the workpiece material to be ground. The converted volume of the removed material is then continuously added by an accumulator 37. A signal corresponding to the added volume Zz of the removed material is then applied to a comparator 38. A standard total volume Z1 of the removed material is preset in a preset circuit 56 and a signal corresponding thereto is also applied to the comparator 38. The comparator 38 generates an output signal for causing the dressing device 8 to dress the periphery of the grinding wheel 42 when the added volume 22 becomes equal to the standard total volume Z1. The accumulator 37 is reset by the output signal of the comparator 38.

As shown in FIG. 6,the sizing device 9 includes a bracket 57 which is secured to a pilot bar 58 which is slidably mounted on the table and to a piston rod 59 of the hydraulic cylinder. A cylinder 62 is bored in a block 60 and slidably receives a guide 61. The block assembly 60 is mounted in an upright position on the bracket 57. A guide pin 63 is attached to the guide 61 and is slidably engaged with an elongated slot 64 provided on the block 60 such that rotation of the block 60 is restricted and the range of the axial movement of the block 60 is determined. A rod 65 extends through a hole 66 which is provided on the block 60 in a direction parallel with the cylinder 62,and is slidably received by a pair of bushings 67 and 68 secured in the hole 66. Rotation of the rod 65 is restricted by the engagement of a pin 69 which is attached to the block 60 through an elongated key way 70 provided on the rod 65. The pair of feelers 41a and 41b are,respectively,secured to the front surface of the block 60 and to the lower end of the rod 65.

A holder 71 is secured to the upper end of the rod 65 and supports a magnetic scale 72 which extends in a direction parallel with the rod 65. A reading head 73 is mounted on the block 60 in such manner that the same may be coaxial with the magnetic scale 72. The mag-' netic scale 72 and the reading head 73 are therefore displaceable with respect to each other in accordance with the relative displacement of the feelers 41a and 41b. Since the magnetic scale 72 and the reading head 73 are conventional and may be,for example,the SONY PRECISION MAGNETIC SCALING SYSTEM sold in Japan by SONY Corporation, they will be described only in brief.

The reading head 73 will generate an output signal every time it detects a unit length which is represented by a periodically alternating reference magnetization placed on the magnetic scale 72. The reading head 73 can also discriminate the direction of the movement of the feelers. As shown in FIG. 2, the output signals generated by the reading head 73 are applied to the counter 46. It should be understood that the number of output signals from the reading head 73 is subtracted from the value or number registered in the counter 46 as the pair of feelers 41a and 41b approach each other and the number of output signals from the reading head 73 is added to the value of the counter 46 as the feelers mutually move apart,so that the counter 46 will successively indicate the distance between the feelers 41a and 41b. e

The rod 65 is connected to a weight 74 through a flexible member 75 which passes around a pair of pulleys 76 and 77 which are rotatably mounted on a case 78 secured to the bracket 57. The weight 74 is slidably engaged with a cylinder 79 which is bored in the case 78. A guide pin 80 is attached to the weight 74 and is slidably engaged with an elongated slot 81 provided on the cylinder 79 such that rotation of the weight 74 is restricted and the range of axial movement of the weight 74 is determined. It should be understood that since the weight 74 is heavier than the rod 65,the lower feeler 41b will be urged to move in an upward direction. The upper feeler 41a is urged to move in a downward direction by the gravity thereof. A solenoid operated valve 82 is provided and if the same shifts to a state opposite to that shown in FIG. 6,pressurized air will be supplied to the cylinders 62 and 79 and therefore the feelers 41a and 4lb will mutually move apart. On the other hand,if the solenoid operated valve 82 is shifted to the state shown in FIG. 6,the cylinders 62 and 79 will communicate with the atmosphere and the feelers 41a and 41b will therefore approach each other so as to come in contact with the workpiece W. A signal representing the engagement of the pair of feelers 41a and 411; with the periphery of the workpiece W is generated by a conventional timer,not shown,which is energized when the solenoid operated valve 82 is shifted tothe state shown in FIG. 6. The timer will generate the engagement indicative signal a predetermined period of time after the solenoid operated valve 82 is shifted.

The grinding machine having an adaptive control system which is constructed as described above will operate in the following manner. Assuming that the dressing device 8 has just dressed the periphery of the grinding wheel 42, then any grinding wheel wear will have been eliminated. After the workpiece W is supported between the spindle head 7 and the tail stock, a starting button,not shown,will be pushed. The sizing device 9 will move toward the workpiece W,and'the solenoid operated valve 82 will then be shifted to the state shown in FIG. 6. The feelers will therefore come in contact with the periphery of the workpiece W, and thereby measure the workpiece diameter do. The operation circuit 36 will calculate the volume Z of the removed material and the multiplier 55 will multiply the calculated volume Z by the coefficient Kw so as to provide the converted volume. The accumulator 38 will then add the converted volume. The workpiece W will be rotated by the hydraulic motor 7b at the rotational frequency n which is calculated by the revolution control device 20.

The wheel head 6 will then be advanced toward the workpiece W at a rapid speed in accordance with the feed pulses applied to the pulse motor 6b by the numerical control system 2. When the current distance L between the grinding surface of the grinding wheel 42 and the axis of the workpiece W becomes equal to the one-half diameter do/2, the comparator 23 will generate an output signal therefrom. The numerical control system 2 will stop furnishing the feed pulses to the pulse motor 6b in accordance with the output signal of the comparator 23. The pulse motor 6b is further furnished with the pulses which are generated by the pulse generator 35 in response to the output signal of the comparator 23. In accordance therewith,the grinding wheel 42 will then be moved in a forward direction and begin to grind the workpiece W,whereby the real unit resistance F/b will be held equal to the current optimum unit resistance fv. When the diameter do of the workpiece W becomes equal to the desired diameter df of the finished workpiece, the comparator 24 will generate an output signal therefrom. The numerical control system 2 will cause the pulse generator 35 to 1 stop generating pulses therefrom in accordance with the output signal of the comparator 24. The numerical control system 2 will then furnish pulses to the pulse motor drive circuit 6a in order to rotate the pulse motor 6b in a reverse direction, and the wheel head 6 will thereby be moved to the retracted position. The ground workpiece can then be removed from the grinding machine, and one grinding cycle will have been completed.

Similar grinding cycles will be repeated until the comparator 38 generates an output signal indicating that the added volume EZ is equal to the standard total volume Z] of the removed material. The dressing device 8 will then dress the grinding wheel 42 and the accumulator 37 will be reset in accordance with the output signal of the comparator 38. The real unit resistance F/b will,of course,be decreased as the amount of grinding wheel wear increases as successive grinding operations take place.

It should be understood that the real unit resistance may be decreased as the added volume of the removed material increases.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims,the invention may be practiced otherwise than as specifically described herein.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

l. A grinding machine comprising:

a bed;

a wheel head slidably mounted on said bed and being provided with a rotatable grinding wheel;

a table slidably mounted on said bed for supporting a workpiece thereon;

power means for moving either said wheel head or said table to perform a grinding operation on the workpiece;

resistance detecting means for detecting a grinding resistance exerted on the grinding wheel and for generating an output proportional to said grinding resistance;

control means for providing necessary control information therefrom;

measuring means for generating an output proportional to the number of grinding operations;

a first operation circuit for calculating a current optimum grinding resistance on the basis of an objective grinding resistance provided by said control means and the output of said measuring means,said current optimum grinding resistance being decreased toward said objective grinding resistance as the output of said measuring means increases; and,

feed control means for operating said power means in a manner such that the grinding resistance exerted on the grinding wheel may be maintained equal to said current optimum grinding resistance.

2. A grinding machine as set forth in claim 1, wherein is further included:

a sizing device for continuously measuring the diameter of said workpiece;

a second operation circuit for calculating the rotational frequency of the workpiece on the basis of a desired peripheral speed for the workpiece provided by said control means and the workpiece diameter measured by said sizing device; and,

driving means for rotating the workpiece in accordance with the rotational frequency calculated by said second operation circuit.

3. A grinding machine as set forth in claim 1, wherein is further included:

a sizing device for continuously measuring the diameter of said workpiece;

a dressing device for dressing a periphery of the workpiece;

a third operation circuit for calculating the volume of material removed from said workpiece on the basis of the workpiece diameter measured by said sizing device before a grinding operation, the desired diameter of the finished workpiece and the width of the part to be ground as provided by said control means;

an accumulator for adding up the volume of the removed material;

a dressing device; and,

a comparator for generating a signal for causing the dressing device to dress the grinding wheel when the added volume stored in said accumulator becomes equal to a standard total volume.

4. A grinding machine comprising:

a bed;

a wheel head slidably mounted on said bed and being provided with a rotatable grinding wheel;

a table slidably mounted on said bed for supporting a workpiece thereon;

power means for moving either said wheel head or said table to perform a grinding operation of the workpiece;

position indicating means for indicating the current distance between the grinding surface of the grinding wheel and the axis of the workpiece;

resistance detecting means for detecting a grinding resistance exerted on the grinding wheel and for generating an output proportional to said grinding resistance;

a sizing device for continuously measuring the diameter of said workpiece;

a divider for calculating one-half of the workpiece diameter;

control means for providing necessary control information therefrom;

measuring means for calculating the difference between said current distance and the one-half of the workpiece diameter in order to measure the amount of grinding wheel wear;

a first operation circuit for calculating a current optimum grinding resistance on the basis of an objective grinding resistance provided by said control means and the amount of grinding wheel wear, said current optimum grinding resistance being decreased toward said objective grinding resistance as the amount of grinding wheel wear increases; and,

feed control means for operating said power means in a manner such that the grinding resistance exerted on the grinding wheel may be maintained equal to said current optimum grinding resistance 5. A grinding machine comprising:

a bed;

a wheel head slidably mounted on said bed and being provided with a rotatable grinding wheel;

a table slidably mounted on said bed for supporting a workpiece thereon;

power means for moving either said wheel head or said table to perform a grinding operation on the workpiece;

resistance detecting means for detecting a grinding resistance exerted on the grinding wheel and for generating an output proportional to said grinding said objective unit resistance as the output of said measuring means increases;

a second operation circuit for dividing said grinding resistance by the width of the part to be groundas provided by said control means in order to calculate the real unit resistance; and,

feed control means for operating said power means in a manner such that said real unit resistance may be maintained equal to said current optimum unit resistance. 

1. A grinding machine comprising: a bed; a wheel head slidably mounted on said bed and being provided with a rotatable grinding wheel; a table slidably mounted on said bed for supporting a workpiece thereon; power means for moving either said wheel head or said table to perform a grinding operation on the workpiece; resistance detecting means for detecting a grinding resistance exerted on the grinding wheel and for generating an output proportional to said grinding resistance; control means for providing necessary control information therefrom; measuring means for generating an output proportional to the number of grinding operations; a first operation circuit for calculating a current optimum grinding resistance on the basis of an objective grinding resistance provided by said control means and the output of said measuring means,said current optimum grinding resistance being decreased toward said objective grinding resistance as the output of said measuring means increases; and, feed control means for operating said power means in a manner such that the grinding resistance exerted on the grinding wheel may be maintained equal to said current optimum grinding resistance.
 2. A grinding machine as set forth in claim 1, wherein is further included: a sizing device for continuously measuring the diameter of said workpiece; a second operation circuit for calculating the rotational frequency of the workpiece on the basis of a desired peripheral speed for the workpiece provided by said control means and the workpiece diameter measured by said sizing device; and, driving means for rotating the workpiece in accordance with the rotational frequency calculated by said second operation circUit.
 3. A grinding machine as set forth in claim 1, wherein is further included: a sizing device for continuously measuring the diameter of said workpiece; a dressing device for dressing a periphery of the workpiece; a third operation circuit for calculating the volume of material removed from said workpiece on the basis of the workpiece diameter measured by said sizing device before a grinding operation, the desired diameter of the finished workpiece and the width of the part to be ground as provided by said control means; an accumulator for adding up the volume of the removed material; a dressing device; and, a comparator for generating a signal for causing the dressing device to dress the grinding wheel when the added volume stored in said accumulator becomes equal to a standard total volume.
 4. A grinding machine comprising: a bed; a wheel head slidably mounted on said bed and being provided with a rotatable grinding wheel; a table slidably mounted on said bed for supporting a workpiece thereon; power means for moving either said wheel head or said table to perform a grinding operation on the workpiece; position indicating means for indicating the current distance between the grinding surface of the grinding wheel and the axis of the workpiece; resistance detecting means for detecting a grinding resistance exerted on the grinding wheel and for generating an output proportional to said grinding resistance; a sizing device for continuously measuring the diameter of said workpiece; a divider for calculating one-half of the workpiece diameter; control means for providing necessary control information therefrom; measuring means for calculating the difference between said current distance and the one-half of the workpiece diameter in order to measure the amount of grinding wheel wear; a first operation circuit for calculating a current optimum grinding resistance on the basis of an objective grinding resistance provided by said control means and the amount of grinding wheel wear, said current optimum grinding resistance being decreased toward said objective grinding resistance as the amount of grinding wheel wear increases; and, feed control means for operating said power means in a manner such that the grinding resistance exerted on the grinding wheel may be maintained equal to said current optimum grinding resistance.
 5. A grinding machine comprising: a bed; a wheel head slidably mounted on said bed and being provided with a rotatable grinding wheel; a table slidably mounted on said bed for supporting a workpiece thereon; power means for moving either said wheel head or said table to perform a grinding operation on the workpiece; resistance detecting means for detecting a grinding resistance exerted on the grinding wheel and for generating an output proportional to said grinding resistance; control means for providing necessary control information therefrom; measuring means for generating an output proportional to the number of grinding operations; a first operation circuit for calculating a current optimum unit resistance on the basis of an objective unit resistance provided by said control means and the output of said measuring means,said current optimum unit resistance being decreased toward said objective unit resistance as the output of said measuring means increases; a second operation circuit for dividing said grinding resistance by the width of the part to be ground as provided by said control means in order to calculate the real unit resistance; and, feed control means for operating said power means in a manner such that said real unit resistance may be maintained equal to said current optimum unit resistance. 